Conventional collapsible steering columns usually include the basic concept of a steering column comprising telescopically engaged upper and lower column tubes, and a steering shaft rotatably disposed within the telescopically engaged upper and lower column tubes. A steering wheel is secured to the rearward end of the steering shaft. The upper column tube is mounted to a steering column support member, usually affixed to the dashboard assembly with a bracket assembly. The bracket assembly generally includes means for absorbing impact loads through plastic deformation as the column tubes move together axially during a collision. Such an arrangement is shown in U.S. Pat. No. 4,627,306 presently assigned to the assignee of the present invention.
In the art of providing a collapsible steering column having a telescopically engaged, relatively collapsible upper and lower column tubes, it is also known to provide the damping means at the lower column tube and to provide that the upper column be connected to a steering column support member by means allowing the upper column tube to slip free of its connection. Such a means may include a clamp permanently fixed to the upper column member and including slip clips or shear modules built within the flange of the clamp that is secured to the column support member. Thus it has been provided that the upper column member upon impact by the driver can be sheared loose of the column support member at this same clamp. Such an arrangement is shown in U.S. Pat. No. 4,274,299 assigned to the assignee of the present invention.
In none of these prior art structures has attention been paid to the problem of assuring that upon impact resulting during a collision the steering column will collapse in an axial manner with minimal interference from the irregularities of the column support member along the collapsible axial extent of the steering column member. In other words, in conventional systems representing the current state-of-the-art, the column support member surface to which the upper column tube of the steering column is bolted is irregular in shape. Thus there would normally appear a number of cavities on what would otherwise be an adjacent abutting surface of the steering column support member. During collision it has been found that these surface irregularities form pockets into which the upper column tube may deform, thus adversely affecting the controlled collapse of the steering column pursuant to its engineered design.
At best it is known that the direction of the axial force caused by the driver colliding with the steering column can be controlled so that the principal force vector is along the axis of the steering column. Such an arrangement is shown in U.S. Pat. No. 4,703,669.